Multipolar residual spiral ganglion neurons

Abstract

Guinea pigs drug deafened with a combination of kanamycin (400 mg/kg S.C.) followed 2 h later with ethacrynic acid (40 mg/kg I.V.) have a stable number of spiral ganglion neurons by 8 months post‐treatment which is 13% of the normal spiral ganglion population [M. Webster and D. B. Webster, Brain Res. 212, 17–30 (1981)]. Three μm serial sections of the spiral ganglion of such drug deafened guinea pigs sacrificed either 9 months or 16 months following treatment were cut. Each section was photographed and the profile of each neuron was traced onto acrylic sheets. Stacking the acrylic sheets allowed a three‐dimensional visualization of each neuron. In the 9‐month post‐treatment animals, the spiral ganglion neuronal types were: 6% unipolar, 53% bipolar, 38% multipolar, and 3% questionable. In the 16‐month post‐treatment animals, the spiral ganglion neuronal types were: 3% unipolar, 17% bipolar, 78% multipolar, and 2% questionable. These data suggest that following long term organ of Corti loss, the residual spiral ganglion neurons sprout new processes. [Work supported by NIH grants NS‐12510 and NS‐11647.]